Method of making cellulose powder



Patented July 11, 1944 UNITED STATES PATENT OFFICE Julius Kent, New York, N. Y., assignor to Kent Chemical Corporation, a corporation of Delaware No Drawing. Application June 18, 1941, Serial No. 398,675

3 Claims.

The present invention relates to cellulose powder and the method of making same. More specifically the invention relates to the kind of powder and the method of making same from fibrous, cellulose material covered by my copending application, Serial No. 341,678, filed June 21, 1940, and assigned to the same assignee as the present application. As disclosed in said ap plication, cellulose fibers may be readily ground or pulverized to a fine powder upon first rendering the fibers brittle by steeping them in certain solutions and subsequently drying the steeped fibers or fibrous, cellulose material.

One object of my invention is to provide an improved, cellulose powder adapted for general use and particularly suitable as an absorptive and antiseptic material.

Another object of my invention is to provide an improved method of making cellulose powder, which method may be carried out economically and efficiently.

This is accomplished in accordance with my invention by the process of rendering cellulose fibers brittle by steeping them in an aqueous, alcoholic or like solution of o-rthoboric acid for a period of time suificient to cause penetration of the fibers and thereafter drying the steeped fibers.

I have found that the use of orthoboric acid solutions in the process of rendering cellulose fibers brittle permits wide variations in the strength of the solutions without materially affecting the degree of brittleness and the quality of the powder produced by grinding the brittle fibers. Due to the small size of the particles the powder has a lower viscosity than the original cellulose fibers. Otherwise the powder has retained substantially all physical and chemical properties of the original cellulose, such as its content of alpha cellulose, its copper figure, etc.

According to my theory, the orthoboric acid contained in the steeped fibers is transformed into meta and tetraboric acids as the fibers are dried at temperatures of about 80 to 140 C. The meta and tetraboric acids may form coatings on the fibers or fill pores or intermolecular spaces therein and thus render the fibers brittle, though it is diflicult to understood that the relatively small amount of boric acid necessary to render the cellulose fibers brittle should be suificient to produce such coatings or fill the pores on the relatively large surfaces of the fibers. It appears more plausible that the brittleness is caused by the formation of compounds of boric acid with the fibrous cellulose which may be in the form of a chemical compound due to a reaction between the free hydroxyl groups of cellulose with boric acid. Such compound may also be in the form of an absorption compound similar to that of alkali cellulose.

After the fibers are pulverized to a fine powder in a pebble mill or like grinding or comminuting apparatus the orthoboric acid may be regained by a washing process, subjecting the powder to water or any suitable organic or inorganic solvent such as alcohol. During the washing process the meta and tetraboric acid are converted into orthoboric acid. The boric acid contained in the powder upon grinding of the brittle cellulose fibers may be retained therein as it will not subsequently chemically act on the cellulose powder. In many instances, especially when the powder is to be used as an absorptive, antiseptic material, it is advantageous to retain the boric acid in the powder.

Example Ramie, cotton linters, wood pulp, cornstalk fibers, rayon waste or like cellulose material are placed into an aqueous or an alcoholic bath of from 2 to 12% orthoboric acid and subjected to such solution for about /2 hour at room temperature. The fibers are then removed from the bath and dried .at a temperature of from to C. and thereafter ground in a pebble mill.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Method of making a highly absorptive antiseptic powder comprising the steps of steeping fibrous cellulose material in a solution of orthoboric acid, drying the steeped material at a temperature of between 80 and 140 C. and grinding the dried material.

2. Method of making cellulose powder comprising the steps of steeping fibrous cellulose material in a solution of orthoboric acid, drying the steeped material at a temperature between 80 and 140 C., grinding the dried material, and removing the boric acid from the ground material.

3. Method of making a highly absorptive antiseptic powder comprising the steps of subjecting fibrous cellulose material to an aqueous solution of from 2% to 12% orthoboric acid for about /2 hour at room temperature, removing the material from the solution and drying it at a temperature of between 80 and 140 C., and pulverizing the dried material.

JULIUS KENT. 

